Chain drives are the predominant means of power transmission on two-wheelers such as bicycles. Chains are also used for power transmission on numerous machines. Very often, the chain sprockets are connected to a shaft via a form-fitting shaft/hub connection. In general, these and other connections work with local elevations and depressions with respect to a cylinder-shaped connection surface. Some free play fit between the shaft and hub is important for the proper function of these connections. However, under load and if tolerances between the shaft and hub are too large, it can lead to wobbling between the two components. This is considered negative. On the other hand high-quality fits are relatively expensive to manufacture using machining processes. This is a disadvantage when one has to manufacture low-cost mass products.
The chain sprocket is usually thin on affordable bikes with hub gears. This component is typically two to three millimeters wide and is usually a stamped part made of steel and has three or more drive cams with teeth which engage grooves which are located on the input shaft of the hub gear. The fit between these two components is usually a clearance fit. This is necessary in order to employ low-cost manufacturing methods such as sintering, casting or stamping. To prevent the sprocket from moving axially on the input shaft, it is typically held in position by a lock washer or snap ring.
In recent years, many chain drives in automotive technology and general drive technology were replaced by toothed belt drives. Advantages include lower weight, longer service life, less noise and operation without lubricant. Especially in the field of bicycles with hub gears, toothed belt drives according to EP000002289792A1, CA000002749293A1 and U.S. Ser. No. 00/000,7854441B2 are becoming more prevalent.
Because a functioning toothed belt drive requires a defined preload on the belt, a wobbling toothed belt disk on the rear hub would not be able to maintain a constant tension. If the toothed belt disk is not centered and tightly fixed on the rear hub, there can be operating noises as the toothed sprocket moves on the input shaft. The consequence can be squeaking and creaking noises.
Rear hubs with hub gears from all major manufacturers have a centering diameter, which, due to low-cost manufacturing methods, have typical tolerances of plus/minus 0.15 millimeters in the area of the input shaft. If one intends to manufacture inexpensive toothed sprockets without machining by sintering or investment casting, then the manufacturing process requires also bore tolerances in the area of plus/minus 0.15 millimeters. Considering the boundary conditions of the assembly both components can thus be combined only with a certain play. This is the problem of deficient centering when using a toothed sprocket with a spline shaft profile in combination with inexpensively available hub gears.
Means are available to absorb excess tolerance in the component fit between a toothed sprocket and a hub gear. The sprocket relies on a bending beam which absorbs the fit tolerance. The art comprises a sprocket having a first radially movable surface which has a diameter slightly smaller than the hub to which it is mounted. A second surface prevents relative rotation of the parts. Representative of the art is US application serial number US20150016880A1 which discloses a shaft/hub connection for vehicles or for use in drive systems with a cylinder-shaped shaft component, containing elevations or depressions on the lateral surface and a hub component having a bore, including inside the bore also elevations or depressions, whereby the shaft component can be mounted inside the bore of the hub component. It is further distinguished in that inside the bore of the hub component at least 2 surfaces are arranged such that an elastic deformation of these surfaces in the radial direction is possible and inside the bore of the hub component at least 2 surfaces are arranged such that an elastic deformation of these surfaces in the radial direction is less possible. In addition, the shaft/hub connection is characterized in that the elastically deformable surfaces are connected in a materially bonding manner with the elastically less deformable surfaces.
What is needed is a toothed sprocket having a first surface disposed on a bending beam and radially moveable, a second surface radially moveable to a lesser extent that the first surface, and a third surface in cooperative relation to a second surface, the third surface bearing upon the outer surface of the input shaft, the third surface having a diameter greater than the diameter of the outer surface. The present invention meets this need.